The orientation of the Amazonian geoglyphs as a clue for their interpretation
This paper analyzes the orientation of 326 Amazonian geoglyphs using remote sensing and archaeoastronomy, revealing a non-random alignment that indicates their builders possessed a significant interest in the Sun's annual cycle.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine you are a detective trying to solve a mystery, but instead of finding fingerprints or footprints, you are looking at giant shapes drawn on the ground. This is the world of archaeoastronomy, a field where scientists act like cosmic detectives. They study ancient buildings and earthworks to see if the people who built them were looking at the sky. The big idea here is simple: if a structure is built to face a specific direction, like the sunrise on the longest day of the year, it might be a giant calendar or a temple for the sun, rather than just a random pile of dirt. We care about this because it helps us understand how ancient people thought. Did they just build things to live in, or did they build them to talk to the stars and track the seasons?
In the middle of the Amazon rainforest, a mystery has been slowly revealing itself. As trees were cut down for farming in the 1970s, huge, strange shapes made of dirt ditches and banks started popping out of the green canopy. These are called Amazonian geoglyphs. They look like giant squares, rectangles, and circles, some connected by straight "roads" of earth. For a long time, nobody knew exactly what they were for. Some thought they were forts, others thought they were graveyards, but no bodies or weapons were found inside.
A researcher named Giulio Magli decided to look at these shapes with a new pair of glasses. Instead of digging in the dirt, he used satellite images from Google Earth to measure the angles of 326 of these square and rectangular earthworks. He wanted to see if they were pointing in random directions or if they were aiming at something specific in the sky.
The results were like finding a secret code. The directions the earthworks were facing were definitely not random. If you threw darts at a board to pick directions, you wouldn't get this pattern. Instead, the builders seemed obsessed with the path of the Sun. The data showed three main "hot spots" where the earthworks were pointing:
- Straight East: Many were aligned almost perfectly with the cardinal directions (North, South, East, West). This suggests the builders cared about the four corners of the world.
- The Summer Sunrise: A big group pointed toward where the sun rises on the summer solstice (the longest day of the year).
- The "Dry Season" Sunrise: Another group pointed to a sunrise that happens around late May or mid-July.
Why does that third one matter? The paper suggests a clever connection to farming. In that part of the Amazon, the heavy rains stop around May. The sun rising on those specific dates would have been a signal to the ancient farmers that the dry season was starting and it was time to harvest their corn. It wasn't just about the winter solstice; it was about the specific day the weather changed.
The paper also argues against some other ideas. It says these probably weren't defensive forts because the ditches are on the inside of the walls (which would be weird for a fort) and no weapons were found. It also says they likely weren't just random piles of dirt; the math proves the builders had a plan.
So, what's the verdict? The paper suggests that these giant Amazonian shapes were likely ceremonial structures. They were built by a complex society that watched the sky closely, using the sun to mark the seasons and the start of the dry season. While we can't be 100% sure of everything because some of these sites are still hidden under the forest, the evidence points to a culture that built giant earth calendars to celebrate the rhythm of the sun and the seasons. To get the full picture, scientists say we'll need to use special laser scanners from the air to see what's still hiding under the trees.
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